ABSTRACT
Cognitive processes and other advanced neural functions rely on spatial and temporal interplay within linked neural networks. To study this interplay and test network level models, imaging techniques are required to capture dynamics of neural interaction. Of the many available imaging techniques, including PET, MRI, MEG, and EEG, recent developments in optical techniques offer signicant advantages and a unique complement to other methods. Much effort has been invested in techniques that use light to acquire images of brain activity. Sensitive optical techniques have demonstrated spatial organization of visual cortex columnar structures in a fashion that complements electrophysiological recording.1-3 Spatial patterns of sensory activation in human temporal cortex4 and rodent sensory cortex5,6 have also been visualized. Thus, hemodynamic and other metabolic indicators have successfully mapped the dynamics of neural activity in vivo using spectroscopic and oximetry techniques.7,8 Light absorbance changes associated with metabolic and hemodynamic processes are robust and relatively easy to obtain noninvasively, but spatial and temporal resolutions are limited by the anatomy and physiological regulation of cerebral perfusion. Fundamentally, the spatial resolution is limited by microvasculature organization, and the temporal resolution is limited by the rate of vessel diameter uctuations and hemoglobin deoxygenation, which can occur as rapidly as 150 to 250 ms.9
